Unit for use in optical analysis

ABSTRACT

A unit for use in optical analysis is adapted to be mounted in a radial position on a centrifuging rotor and comprises a straight tubular cell. One end of the tubular cell is open and the other end is closed by an optically transparent wall which is substantially perpendicular to the longitudinal axis of the cell. The cell receives one component of a solution to be optically analysed and a second component of the solution is received in a recess of a cover of the unit releasably secured in a position closing the open end of the cell. The cover is formed with an aperture connecting the recess of the cover to the cell in the closed position, so that the second component can flow into the cell during centrifuging.

BACKGROUND

This invention relates to a unit for containing a solution to beoptically analyzed.

It has already been suggested that a number of small containers orreceptacles be placed on a rotor and a solution in each receptacle beanalyzed photometrically by means of a light beam which intersects thepath described by the receptacles and by measuring the intensity of thelight beam issuing from each receptacle.

A known analyser employing this suggestion comprises a rotor which isformed with a number of radial recesses each communicating with ananalysis receptacle disposed at the outside end of the recess. Each suchrecess is divided into at least two compartments adapted to receive aproduct for analysis and at least one reagent, respectively. Thecentrifugal force arising from rotation of the rotor has the effect ofdisplacing the liquid from the inner compartment towards the outercompartment and then of transferring the resulting mixture to theanalysis receptacle.

The main disadvantage of such rotorsis that they need cleaning aftereach analysis before being reused, so that the time wasted isconsiderable in respect of both cleaning and loading the apparatus withthe reagents and samples.

In endeavours to obviate this disadvantage a rotor based on the sameunderlying idea but which is discarded after use and which is mountedreleasably on a rotating support was studied. Such rotors are relativelycostly, and so it is a costly business to use a new rotor for each newseries of analyses.

Yet another disadvantage is the design of the analysis receptacle. Thelight beam passes through only some of the solution to be analyzed inall the receptacles, and so the number of molecules which are to bedetected and which the light beam encounters depends upon theconcentration of the mixture and upon the thickness of the layer ofliquid through which the light beam passes. Consequently, the quantityof the sample, the quantity of the or each reagent and vessel dimensionsare further factors affecting measurement accuracy.

SUMMARY

It is an object of the invention to increase the speed and flexibilityof operation of such optical analyzers. It is another object of theinvention to improve the accuracy of analysis by making analysis lessdependent on measurement accuracy factors. It is another object of theinvention to provide a solution of the problem which is moreadvantageous economically than the former solutions.

Accordingly, the present invention provides a unit for containing asolution to be optically analyzed and for mounting in a radial positionon a centrifuging rotor, which unit comprises a straight tubular cellfor containing a first component of the solution and having one end openand the other end closed by an optically transparent wall which issubstantially perpendicular to the longitudinal axis of the cell, acover and means releasably to secure the cover in a position closing theopen end of the cell, the cover being formed with a recess forcontaining a second component of the solution and with at least oneaperture connecting the said recess to the cell in the closed position,through which aperture the second component can flow into the cellduring centrifuging.

BRIEF DESCRIPTION OF DRAWINGS

In order that the invention may be readily understood, an embodimentthereof will now be described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a plan view of an analyzer apparatus in which units embodyingthe invention are employed;

FIG. 2 is a sectional view on line II--II of FIG. 1;

FIG. 3 is a view corresponding to part of FIG. 2 and showing theapparatus during the analysis phase;

FIG. 4 shows the rotor separately from the apparatus during the chargingor loading phase;

FIG. 5 is a block schematic diagram of a control circuit for theapparatus; and

FIGS. 6 to 11 are sectional views of an analysis unit embodying theinvention during various phases of the analysis procedure.

DESCRIPTION OF PREFERRED EMBODIMENTS

The apparatus shown in FIGS. 1 to 3 comprises an outer casing 1 dividedby a horizontal partition 4 into two chambers 2, 3 disposed one abovethe other. The top chamber 2 serves as a tank or vat for a purpose to bedescribed hereinafter, and the bottom chamber 3 houses a d.c. drivingmotor 5 having a tubular shaft 6 extending through partition 4.Extending around shaft 6 is a sleeve 7 which is secured to partition 4and which carries at its top end a bearing 8 for shaft 6. The top end ofshaft 6 projects beyond sleeve 7 and is rigidly secured to a circularcage 9 which is coaxial with shaft 6 and which extends towards thebottom of the chamber 2. Cage 9 is trunco-conical in shape, with theapex of the cone directed downwardly. The top of the cage, which isconnected to shaft 6, is formed with a number of orifices 9a and thebase of the cage defines with the sleeve 7 an annular orifice 9b. Thefunction of these orifices will be described hereinafter. Extendingaround the outer top edge of cage 9 are a number of resilient clampingmembers or grippers, comprising upwardly extending resilient arms 10which exert a gripping force operative radially towards the axis of cage9. Each arm 10 terminates in an internal enlargement 10a.

The resilient arms 10 releasably secure an analysis rotor 11 to the cage9. The rotor 11 accordingly has a mounting collar 12 which can be seenin FIG. 4 and which is adapted to force aside the arms 10 and engage inthe gripping members when a downwards axial pressure is applied to therotor 11 after the same has been placed on top of the cage 9. The collar12 also has an external bead adapted to engage below the enlargement 10aof each arm 10.

The rotor 11 flares away from the collar 12, the flared part terminatingin a rising vertical annular partition 13 merging into a horizontalannular partition 14 which extends back towards the interior of therotor and which merges into a second descending vertical annularpartition 15, to bound an annular chamber 16. The two partitions 13, 15are apertured, each aperture in one partition being centred on a radiuscommon to one of the apertures in the other partition. Gaskets 46 extendaround the orifices of the outer wall 13.

Each pair of apertures centred on a common radius is adapted to receivea tubular analysis unit 17 which is loaded, for optical analysis, with asolution. Such unit will be described in greater detail hereinafter.

An annular element 18 extends parallel to and above the flared part ofrotor 11 and cooperates with the latter part to bound a passage betweenthe cage orifices 9a and the annular chamber 16. Element 18 is securedto rotor 9 by way of vertical tubes 19 which extend through the flaredpart of the rotor.

Casing 1 is formed with a window 20 whose axis is coplanar with the pathfollowed by the longitudinal axis of the tubular analysis units 17 onrotation of rotor 11. A light source, in the form of a bulb 21 and alens 22, is mounted outside the casing 1 and is adapted to transmit alight beam along the axis of window 20. A light detector in the form ofa photomultiplier 23 is secured to the end of an arm 47 pivoting in avertical plane around an axis perpendicular to the axis of window 20.The arm 47 can be pivoted between two end positions, namely a loweredposition, in which the cell of detector 23 is disposed on the axis ofthe beam from bulb 21, as shown in FIG. 3, and a raised position, inwhich the cell of detector 23 is in a position remote from the rotor 11,as shown in FIG. 2. Accordingly, arm 47 has a quadrant rack or the like50 meshing with a worm 51 rigidly secured to the drive shaft of a motor52.

Each unit 17 comprises two parts, one of which is an analysis cell orenclosure 24 constituted by a cylindrical tube closed at one end by aflat end wall perpendicular to the longitudinal axis of the tube. Thetube 24 is made of a transparent substance such as glass or atransparent plastics. Alternatively, only the end wall need betransparent and can be fitted to the tube. In all cases, the end wall ispreferably recessed from the tube end. The second part of unit 17 is acover 25 constituted by a second tube which is closed at one end andwhose other end has a portion of an outer diameter corresponding to theinner diameter of the open end of the first tube (FIG. 7). Such portion,which is adapted to engage in the first tube 24, terminates in a bearingsurface 25a which can be seen in FIG. 10 and which limits the extent towhich cover 25 can enter unit 24. Cover 25 is made of a soft materialwhich can be perforated by a hollow metal needle, such as an injectionneedle, for a purpose to be described hereinafter. Cover 25 need not betransparent. Unit 24 and cover 25 are of substantially the same volumeas one another.

The analyzer shown in FIG. 2 also comprises a cover ejection mechanism,in the form of a disc 26 rigidly secured to a rod 27 received in theaxial passage extending through shaft 6. Rod 27 projects below motor 5and carries a grooved disc 28 visible in FIG. 2. One end of a lever 29is engaged in the groove of disc 28, the other end of lever 29 beingpivotally connected to the core of a solenoid 30. Between its two endslever 29 is pivotally connected to a horizontal pivot pin rigidlysecured to casing 1. When in its normal position, shown in solid linesin FIG. 2, disc 26 acts as a support for the covers 25 for a purpose tobe described hereinafter; when in its ejection position, shown inchain-dotted lines, disc 26 disengages the covers 25 from the units 24.

There is a heater 31 at the bottom of tank 2 and the side wall thereofhas a cooling circuit 32 connected e.g. to a source of cold water (notshown). Two temperature detectors 33,34 are disposed in the tank 2 andat the exit, respectively, of the rotor tubes 19.

The system represented in the block schematic diagram of FIG. 5 providessupervision and control of the temperature of the bath in the tank 2 andthe control of the various mechanisms of the complete apparatus. Formingpart of the system of FIG. 5 is an automatic sequence control device 35for the analysis procedure, such device being connected by way of aninput E₁ to a start button (not shown), the six outputs of the deviceserving to control the various mechanisms of the apparatus. One outputS₁ is connected to the input of an information-acquiring element 36,outputs S₂ and S₃ are connected to a control amplifier 37 for motor 5,one output S₂ operator the amplifier 37 on d.c. and the other output S₃operates the amplifier 37 on d.c., the output S₅ controls an amplifier48 connected to solenoid 30, the output S₄ controls an amplifier 53energizing motor 52, and output S₆ controls a supervisory element 38 forthe temperature of the bath in tank 2. By way of an amplifier 39 theelement 38 receives the average of the temperatures detected by thedetectors 33, 34 and, depending upon the reference temperature set up atthe output of the control 35, element 38 energizes either the heatingamplifier 40 or the cooling amplifier 41, connected to the heater 31 andcooling circuit 32 respectively, so as to stabilize the average of thetemperatures detected by the detectors 33 and 34 at a valuesubstantially equal to the reference temperature of the control device35.

Rotor shaft 6 which is also the output shaft of motor 5, is rigidlysecured to two tracks 42a, 42b adapted to produce pulses in twophotodetectors 43a, 43b respectively which are connected to the input ofan amplifier 43c, the outputs thereof being connected to theinformation-obtaining element 36. The photodetectors 42a, 42b areadapted to deliver sync pulses to element 36. Accordingly, the firsttrack 42a, which is associated with photodetector 43a, has one mark perunit 17 whereas the second track 42b, associated with photodetector 43b,has one mark for each revolution of the rotor 11, such mark serving toidentify the first unit 17 and therefore the following units 17.Identification is by means of a counter which forms part of the element36 and which is zero reset at each revolution by the track 42b and whichthen counts each pulse produced as each mark of track 42a passes by thephotodetector 43a.

Bulb 21 is connected to a stabilized power supply 44, andphotomultiplier 23 is connected to a high-voltage power supply 45. Theinput of an amplifier 49 of photomultiplier 23 is also connectedthereto, the output of amplifier 49 being connected to the input ofelement 36. Because of the sync signals from photodetector 43a, only thedata concerning the various samples are delivered at output S of element36 whenever a sample passes by the photomultiplier 23, and each dataitem is identified with a specific sample through the agency of thesecond track 42b which indicates the passage of the first sample onceper revolution of the rotor 11, as hereinbefore described.

Now that the apparatus has been described, a description will be givenof the various phases occurring throughout the analysis procedure,reference being made more particularly to FIGS. 6 - 11 which show theunit 17 during various phases of the procedure.

Referring to FIG. 6, reagent is placed at the bottom of the cell 24, bymeans of a pipette if the reagent is a liquid. Only the delivery end ofthe pipette is visible in FIG. 6, the pipette not forming part of thisinvention. Of course, solid reagents, e.g. in AFD form, can also beused, and so the units 17 can be prepared ready supplied with the oreach required reagent. This step can be performed during the manufactureof the unit 17. After the reagent has been introduced in one form oranother, cover 25 is engaged in the aperture of enclosure 24 in themanner shown in FIG. 5.

Rotor 11 is then loaded by the unit 17 being introduced from the outsideand moved towards the rotor axis into the position shown in FIG. 8.Gasket 46 clamps cell 24 so that wall 13 of the annular chamber 16 issealed.

As can be seen in FIG. 4, the positioning of unit 17 ejects thepreviously used cell 24. As can also be gathered from FIG. 4, the unitsare placed on the rotor 11 preferably before the same is mounted on thecage 9 -- a considerable advantage since a number of rotors can beprepared beforehand without any need to stop the analyzer.

Rotor 11 can then be secured to cage 9 for the loading of the samples.As FIG. 2 shows, once the rotor 11 has been mounted on cage 9 the covers25 are supported by disc 26. As FIG. 8 shows, the cover 25 can then bepierced by two hollow needles A₁, A₂, the needle A₁ being the deliveryend of a pipette (not shown) while needle A₂ is simply a vent. Theliquid sample E which it is required to analyse, plus some water fordilution, are introduced through needle A₁. Introducing the sample via aneedle which has penetrated the wall of cover 25 has the veryconsiderable advantage of cleaning the outside of the needle tip, theinside of the needle being cleaned when the dilution water isintroduced. The latter also ensures that all the sample has beenintroduced into the unit 17.

The inner diameter of cover 25 is such that the surface tension of theliquid introduced forms a meniscus which prevents the liquid fromflowing into the analysis cell 24. It is found that all the sample andall the water are contained in cover 25, and this is the reason why thecover 25 is of substantially the same volume as the enclosure 24.

Once all the samples have been transferred into the respective analysisunits 17, a brief centrifuging transfers the liquids into the cells 24where they contact the liquid or AFD reagents (FIG. 9), whereafter thesolution is mixed and homogenized. To this end, the automatic sequencecontrol device 35 shown in FIG. 5 delivers a signal at its output S₃ forthe amplifier 37 to energize motor 5 on a.c. Since motor 5 is a d.c.motor, when it is energized on a.c. it oscillates the shaft 6 at thesame frequency as the a.c. used to energize motor 5. The oscillatingmotion of rotor 11 causes intense agitation of the liquids or of theliquids and solid reagent in the units 17, as shown in FIG. 10, theagitation mixing the liquids and/or dissolving the solid reagent in theliquid.

Motor 5 is then energized on d.c. to centrifuge the solution, motor 5rotating the rotor at a speed of approximately 1000 r.p.m. The purposeof such centrifuging is to degas the solution by expelling bubbles whichare lighter than the liquid. The bubbles are the result of the liquidbeing agitated. Another effect of the centrifuging is that all thesolution is transferred to the analysis cell 24. The covers 25 are thenejected by operation of solenoid 30 which acts by way of lever 29 toraise the disc 26.

Cell 24 is ready for optical analysis of the solution in it. To thisend, a controlled-temperature water-circulation circuit is providedwhich can bring the solution to an appropriate temperature during themeasurement process. Water is introduced into tank 2 and, through theannular orifice 9b visible in FIGS. 2 and 3, enters cage 9. The watertherein experiences centrifugal force as cage 9 rotates and, because ofthe trunco-conical shape of cage 9, a layer of water forms on the insidetrunco-conical surface of cage 9, is hurled through the orifices 9a andreaches the rotor passage bounded by the flared part of the rotor andthe annular element 18 and enters the annular chamber 16 through whichthe cells 24 pass. The excess of water arriving continuously in chamber16 returns through the discharge or drain tubes 19 to tank 2. Because ofthe centrifugal force which produces the flow through thewater-circulation circuit, the water leaving the tube 19 is hurledoutwards. Consequently, the detector 34 which is disposed below andinside the exit end of the tubes 19, receives the stream of waterissuing therefrom and can measure the temperature of such water. Thecircuit has other uses, as in centrifuges or any other use where a rotoris involved.

For optical analysis of the solutions in each cell 24, the controldevice 35 transmits a signal to amplifier 53 which starts motor 52, thesame driving worm 51 to lower the arm 47 carrying photomultiplier 23into the position shown in FIG. 3. Each mark on the first track of thephotodetector 42a causes a data item to be delivered at output S ofelement 36. The width and the position of the respective marks on thefirst track of photodetector 42a are such that the data item outputcorresponds to the instant of time when the longitudinal axis of thecell 24 coincides with the axis of the light beam which the bulb 21emits and which the photomultiplier 23 detects.

One of the considerable advantages of the analysis provided by theapparatus described is that the length of the layer of the solution incell 24 through which the light beam passes is proportional to thevolume of the solution. Accuracy ceases to be dependent upon thequantities of reagents in the solution, the only factors which are nowconcerned in accuracy being the quantity of samples and the diameter ofthe cell 24. Also, since the cover 25 is ejected, the distance betweenthe light source 21 and the photomultiplier 23 when the same is in itslowered position is appreciably less than the total length of theanalysis unit 17.

The reusable rotor 11 is removed from the apparatus for loading. Onlythe units 17 are changed for each analysis. The units 17, being closedunits, can, with advantage, be pre-loaded in a series productionoperation with AFD reagents or appropriate liquids for the requiredanalysis. All that the operator in charge of the analysis then has to dois to carry out the operations shown in FIGS. 6 and 7 and the operatorcan directly load the rotor 11 as shown in FIG. 4, whereafter heperforms the other operations shown in FIGS. 8 to 11. Of course, theoperator may have a number of rotors 11 available for a single analyzer,in which event he can prepare a number of rotors in advance withoutstopping the analyzer.

Another great advantage of the apparatus described is the system oftemperature stabilization using a constantly renewed water bath aroundthe cell 24 during analysis. The water temperature is under continuoussupervision and the water is renewed for as long as the rotor 11rotates.

The design of the charging and analysis unit 17 also has advantages. Theunit 17 is of low cost and can therefore be discarded after use. Anotheradvantage of the units 17 is the perforable cover 25 which acts as astorage cell before the sample and reagent are mixed together. Also, thecover 25 prevents any loss of solution when the rotor 11 is oscillated,as shown in FIG. 9. The advantage of the perforable cover 25 inconnection with outside cleaning of the tip of the charging or loadingneedle has already been mentioned. Yet another advantage of the units 17is that the cover 25 is readily removable once mixing and homogenizationof the solution are finished. Also, since the end wall of the analysiscell 24 is recessed from the tube end and the same forms the window forthe entry or exit of the light beam (depending on whether the lightsource is inside or outside the rotor), such end member is protectedduring handling from soiling and scratching likely to reduce itstransparency and therefore impair the accuracy of measurement.

We claim:
 1. A unit for containing a solution to be optically analysedand for mounting in a radial position on a centrifuging rotor, whichunit comprises: a straight tubular cell for containing a first componentof the solution and having one end open and the other end closed by anoptically transparent wall which is substantially perpendicular to thelongitudinal axis of the cell; a cover for closing the open end of saidcell; and means releasably to secure the cover in a position closing theopen end of the cell; the cover being formed with a recess forcontaining a second component of the solution and with at least oneaperture connecting the said recess to the cell in the closed position,through which aperture the second component can flow into the cellduring centrifuging.
 2. A unit according to claim 1, wherein the celland the cover are constituted by two straight tubular members nestingone in the other.
 3. A unit according to claim 2, wherein the cell andthe cover are of substantially the same volume as one another.
 4. A unitaccording to claim 2, wherein the optically transparent wall is recessedrelative to the end of the tubular member which constitutes the cell. 5.A unit according to claim 1, wherein the cover is made of a materialwhich can be cold pierced by a metal point.